ABSTRACT: We investigate the relationship between public and private enforcers introducing a more differentiated approach. In contrast to the existing literature, we take into account that the costs and benefits of detection and prosecution and, thus, the usefulness of each enforcement mode may change with a variation of the type of anticompetitive conduct. We define a set of parameters that determine the costs and benefits of both types to enforce the antitrust laws and discuss implications for European competition law and policy.